brian john
Senior Member
- Location
- Leesburg, VA
The 3 phase primary 208 for the transformer is from a 3 phase 4 wire wye, feeding a why primary (X1, X2, X3) and the secondary is a delta 3 phase (H1, H2, H3)
Even though a neutral was not brought to the transformer on the 208 volt side, it effectively was connected because the XO bond was still connected to ground, which in turn is connected to the neutral back at the service.
voltage x1-x2?
voltage x2-x3?
voltage x1-x3?
voltage x1 to 4rth wire (ground/nuetral)?
I thought it was pretty clear in the OP. 208/120 back fed transformer supplied with L1,L2, and L3 of a 208/120 system. XO happened to be bonded. Even though a neutral was not run the equipment grounding conductor and every other conductive path connected to it carried neutral current.
Simple solution is that the XO needed to be un-bonded and left to float.
Many people have posted this scenario in the past - most of them usually destroyed the transformer. They always end up being told to never connect anything to XO, as undesired current will flow if you do use XO.
Yes there is a compelling reason for it to burn up, as I have outlined above.Telling the input power source and voltages should help explain the X0 problem; if indeed the power source is 208v grounded wye then there is no reason for the X0 on this transformer to burn up...
I would say it will depend on loading conditions. If there is a heavy load on one coil it is going to draw current from both the other phases to provide what is needed to supply the load, but we have that vector math involved in determining exactly how much comes from where, if the XO is connected to the neutral of the supply and one coil is heavily loaded we pretty much have a two wire circuit involved there.In the example for this thread (208Y/120 is the X side of the transformer and is also the input side), let's say the XO is not connected and the bonding jumper is removed (so it is completely isolated/floating).
What voltage would you read from the XO to any of the other X terminals?
With a perfectly balanced load X0-X? = 120V. An unbalanced load may cause the X0 point to move just like the neutral point on a 120/240V circuit where the source neutral conductor has been 'opened'.In the example for this thread (208Y/120 is the X side of the transformer and is also the input side), let's say the XO is not connected and the bonding jumper is removed (so it is completely isolated/floating).
What voltage would you read from the XO to any of the other X terminals?
Just to be pickey.
I know we say X-oh, but the correct terminology should be X-zero. The first character is a letter, the second is a number.
That won't work for users of the NEC unless you get 450.3 re-written.... The confusion in using primary and secondary is not uncommon, it is why I prefer the more universal acceptance adopted by IEC and simply state HV or LV windings and not use terms primary and secondary.
That won't work for users of the NEC unless you get 450.3 re-written.
That won't work for users of the NEC unless you get 450.3 re-written.
It was commented that these terms are not defined, but I wanted to show they do have designations in the standards. The confusion in using primary and secondary is not uncommon, it is why I prefer the more universal acceptance adopted by IEC and simply state HV or LV windings and not use terms primary and secondary.
Just to be pickey.... (i.e. http://www.acmepowerdist.com/pdf/Page_6-16.pdf). ...
i.e., abbreviation for Latin id est, meaning "that is; in other words"
e.g., abbreviation for Latin exempli gratia, meaning "for example"
Just to be pickey.
I know many people besides yourself use "i.e." when presenting an example, but the more "proper" abbreviation "e.g." should be used.
Thank you.:thumbsup:
You made me go look it up. You are correct, effectively i.e. is used instead of "in other words" and e.g. is used instead of "for example".